Search

We searched for the α condensed state in 13C by measuring the α inelastic scattering at Eα = 388 MeV at forward angles including 0 degrees. We performed the distorted wave Born-approximation calculation with the single-folding potential and the multipole decomposition analysis to determine the isoscalar transition strengths in 13C. We found a bump structure around Ex = 12.5 MeV consisting of several 1/2− states, which were excited by the isoscalar monopole (IS0) transitions from the ground state. We proposed that this bump was due to the mirror state of the 13.5 MeV-state in 13N, which dominantly decayed to the α condensed state in 12C. Although this bump was speculated to be a candidate for the α condensed state, the OCM calculation suggested that the α condensed state is unlikely to emerge as the negative parity states. We also found two 1/2+ or 3/2+ states at Ex = 14.5 and 16.1 MeV excited by the isoscalar dipole (IS1) transitions. We compared the experimental level diagram and the IS0 and IS1 transitions strengths with those predicted by shell-model and cluster-model calculations. We suggested that the 16.1-MeV state is a possible candidate for the α condensed state predicted by the cluster-model calculations. However, the theoretical IS1 transition strength for this state is significantly smaller than the measured value. Further experimental information is strongly desired to establish the α condensed state in 13C.

The (Be-10; B-10* [1.74 MeV]) charge-exchange reaction at 100 AMeV is presented as a new probe for isolating the isovector (Delta T = 1) nonspin-transfer (Delta S = 0) response of nuclei, with Si-28 being the first nucleus studied. By using a secondary Be-10 beam produced by fast fragmentation of O-18 nuclei at the NSCL Coupled Cyclotron Facility, applying the dispersion-matching technique with the S800 magnetic spectrometer to determine the excitation energy in Al-28, and performing high-resolution gamma-ray tracking with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to identify the 1022-keV gamma ray associated with the decay from the 1.74-MeV T = 1 isobaric analog state in B-10, a Delta S = 0 excitation-energy spectrum in Al-28 was extracted. Monopole and dipole contributions were determined through a multipole-decomposition analysis, and the isovector giant dipole resonance and isovector giant monopole resonance (IVGMR) were identified. The results show that this probe is a powerful tool for studying the elusive IVGMR, which is of interest for performing stringent tests of modern density functional theories at high excitation energies and for constraining the bulk properties of nuclei and nuclear matter. The extracted distributions were compared with theoretical calculations based on the normal-modes formalism and the proton-neutron relativistic time-blocking approximation. Calculated cross sections based on these strengths underestimate the data by about a factor of 2, which likely indicates deficiencies in the reaction calculations based on the distorted wave Born approximation.

International audience; The (Be10,B*10[1.74 MeV]) charge-exchange reaction at 100 AMeV is presented as a new probe for isolating the isovector (ΔT=1) nonspin-transfer (ΔS=0) response of nuclei, with Si28 being the first nucleus studied. By using a secondary Be10 beam produced by fast fragmentation of O18 nuclei at the NSCL Coupled Cyclotron Facility, applying the dispersion-matching technique with the S800 magnetic spectrometer to determine the excitation energy in Al28, and performing high-resolution γ-ray tracking with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to identify the 1022-keV γ ray associated with the decay from the 1.74-MeV T=1 isobaric analog state in B10, a ΔS=0 excitation-energy spectrum in Al28 was extracted. Monopole and dipole contributions were determined through a multipole-decomposition analysis, and the isovector giant dipole resonance and isovector giant monopole resonance (IVGMR) were identified. The results show that this probe is a powerful tool for studying the elusive IVGMR, which is of interest for performing stringent tests of modern density functional theories at high excitation energies and for constraining the bulk properties of nuclei and nuclear matter. The extracted distributions were compared with theoretical calculations based on the normal-modes formalism and the proton-neutron relativistic time-blocking approximation. Calculated cross sections based on these strengths underestimate the data by about a factor of 2, which likely indicates deficiencies in the reaction calculations based on the distorted wave Born approximation.

International audience; A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction He4(He8,Be8) at 186 MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst) MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (He8,Be8) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of Pb-208 shows that, at very forward angles, J(pi) = 1(-) states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9MeV; that is, in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the E1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR.

A benchmark experiment on Pb-208 shows that polarized proton inelastic scattering at very forward angles including 0 degrees is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.021)(+0.025) fm in Pb-208 derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.

A benchmark experiment on 208Pb shows that polarized proton inelastic scattering at very forward angles including 0{\deg} is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r_skin = 0.156+0.025-0.021 fm in 208Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence, relevant to the description of neutron stars., Comment: 5 pages, 5 figures, revised mansucript

Vector analyzing power for the proton-6He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target working at low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The alpha-core distribution in 6He is suggested to be a possible key to understand the nuclear structure sensitivity., 5 pages, 3 figures, accepted for publication as a Rapid Communication in Physical Review C

On March 23, 2009, the first beam was successfullytransported to the final focal plane of the SHARAQspectrometer. We investigated detector responses toheavy-ion beams and the ion optical properties ofthe SHARAQ spectrometer1) and the high-resolutionbeam line2) in the subsequent commissioning runs andfound that the system as a whole worked almost as perits design. The first physics run with the spectrometerwas performed in November 2009. In this article, wereview the progress in the SHARAQ project in 2009.

The deuteron to proton polarization transfer coefficients K-yy(y') and K-y(y') together with the deuteron analyzing powers are measured in three coplanar configurations of the deuteron-proton breakup reaction with a 135-MeV/nucleon polarized deuteron beam at the RIKEN Accelerator Research Facility. The data are compared with theoretical predictions based on exact solutions of the three-nucleon (3N) Faddeev equations with high-precision nucleon-nucleon (NN) forces, alone or combined with two 3N force (3NF) models, the 2 pi-exchange Tucson-Melbourne(')(99) (TM(')99) and Urbana IX. Large 3NF effects have been found for all the measured observables. Predicted effects are supported by the data, with the exception of the vector analyzing power A(y)(d). For this observable, theory based on only NN forces is sufficient to explain the data. The behavior of the breakup analyzing powers is found to be different from the corresponding observables in elastic nucleon-deuteron scattering.

The vector analyzing power has been measured for the elastic scattering of neutron-rich ^He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a ^He nucleus. An optical model analysis revealed that the spin-orbit potential for ^ He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with an α+n+n cluster folding model suggests that the interaction between a proton and the α core is essentially important in describing the p+^He elastic scattering. The data are also compared with fully microscopic analyses using nonlocal optical potentials based on nucleon-nucleon g matrices.